Feature/Chore: Replaces all usages of ImageMagik's convert binary with a simple Pillow based helper

This removes ImageMagik as a dependency entirly and all documentation is cleaned up from it.
We no longer need to install it, have a policy for it to allow PDFs and no longer shell
out to it either.

docs/configuration.md

@@ -1873,7 +1873,10 @@ the literal path for that program.
 
 #### [`PAPERLESS_CONVERT_BINARY=<path>`](#PAPERLESS_CONVERT_BINARY) {#PAPERLESS_CONVERT_BINARY}
 
-: Defaults to "convert".
+!!! warning
+
+    Deprecated and has no effect, since Paperless-ngx no longer uses
+    ImageMagick. It will be removed in a future release.
 
 #### [`PAPERLESS_GS_BINARY=<path>`](#PAPERLESS_GS_BINARY) {#PAPERLESS_GS_BINARY}